Time-interleaved noise-shaping successive-approximation analog-to-digital converter

ABSTRACT

A time-interleaved noise-shaping successive-approximation analog-to-digital converter (TI NS-SAR ADC) is shown. A first successive-approximation channel has a first set of successive-approximation registers, and a first coarse comparator operative to coarsely adjust the first set of successive-approximation registers. A second successive-approximation channel has a second set of successive-approximation registers, and a second coarse comparator operative to coarsely adjust the second set of successive-approximation registers. A fine comparator is provided to finely adjust the first set of successive-approximation registers and the second set of successive-approximation registers alternately. A noise-shaping circuit is provided to sample residues of the first and second successive-approximation channels for the fine comparator to finely adjust the first and second sets of successive-approximation registers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.16/990,016, filed on Aug. 11, 2020, now U.S. Pat. No. 11,043,958, whichclaims the benefit of U.S. Provisional Application No. 62/924,243, filedon Oct. 22, 2019, the entirety of which is incorporated by referenceherein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to analog-to-digital converters (ADCs).

Description of the Related Art

Recently, the number of smart devices and the amount of data transferare growing at an unprecedented rate. To provide users with ahigh-quality experience, wireless local area network (WLAN) plays a keyrole among wireless standards. Wifi 6 enhances spectrum efficiency,increases data rate, and serves more users simultaneously in publicareas. To support 1024 Quadrature amplitude modulation (QAM) in a 160MHz radio frequency (RF) signal bandwidth while retaining sufficienterror vector magnitude (EVM), the ADC has to achieve in-band dynamicrange (DR) of 63-70 dB over 80-MHz baseband bandwidth.Successive-approximation analog-to-digital converters (SAR ADCs) areused extensively in Wifi applications due to their low power and smallfootprint. For DR >60 dB, quantization noise and comparator noise becomethe dominant noise sources. Recently, noise-shaping (NS) SAR ADCs havebecome popular to increase signal-to-noise ratio (SNR), whichconsiderably reduce these two noise sources.

A basic concept of SAR ADC is described in this paragraph. During aninput sampling phase, an input voltage V_(I) is sampled onto a weightedcapacitor array (capacitive digital-to-analog converter, abbreviated toCDAC). During an analog-to-digital conversion phase, asuccessive-approximation scheme is performed. The CDAC is controlled tosuccessively approximate its positive and negative output terminals. Acomparator compares the positive and negative output terminals of theCDAC and, accordingly, successively adjusts a set ofsuccessive-approximation registers (e.g., a SAR logic). The values ofthe set of successive-approximation registers are fed back to the CDACto control the successive-approximation between the positive andnegative output terminals of the CDAC. According to a series ofcomparator outputs generated during the successive approximation, thecapacitors within the CDAC are switched between several referencevoltages to equalize the voltage levels at the positive and negativeoutput terminals of the CDAC, and the digital representation of theinput voltage V_(I) is determined from the MSB (most significant bit) tothe LSB (least significant bit) of the set of successive-approximationregisters.

However, a residue voltage VR may still exist between the positive andnegative output terminals of the CDAC after the successiveapproximation. A noise-shaping signal may be derived from the residuevoltage VR for noise elimination. The comparator of the SAR ADC usuallyprovides an additional differential input pair for subtraction of thenoise-shaping signal. The additional differential input pair, however,may contribute extra thermal and kickback noise. Furthermore, thegeneration of the noise-shaping signal may involve an active residueamplification (using an op amp), which consumes a lot of power.

An efficient, low power, small area, high-speed, and wide bandwidthNS-SAR ADC is called for.

BRIEF SUMMARY OF THE INVENTION

A fully passive, time-interleaved (TI) noise-shapingsuccessive-approximation analog-to-digital converter (NS-SAR ADC) isshown, which employs a passive (without an op amp) signal-residuesummation technique and 2-way time-interleaving. The signal bandwidth isdoubled while keeping the same dynamic range (DR) and figure-of-merit(FoM) versus a single-channel counterpart. A shared fine comparatorreduces interleaving spurs.

A TI NS-SAR ADC in accordance with an exemplary embodiment of thepresent invention includes a first successive-approximation (SAR)channel, a second successive-approximation channel, a fine comparator,and a noise-shaping circuit. The first successive-approximation channelhas a first set of successive-approximation registers (e.g. SAR logic),and a first coarse comparator operative to coarsely adjust the first setof successive-approximation registers. The secondsuccessive-approximation channel has a second set ofsuccessive-approximation registers (e.g. another SAR logic), and asecond coarse comparator operative to coarsely adjust the second set ofsuccessive-approximation registers. The fine comparator is operative tofinely adjust the first set of successive-approximation registers andthe second set of successive-approximation registers alternately. Thenoise-shaping circuit samples residues of the firstsuccessive-approximation channel for the fine comparator to finelyadjust the second set of successive-approximation registers, and samplesresidues of the second successive-approximation channel for the finecomparator to finely adjust the first set of successive-approximationregisters.

In an exemplary embodiment, the noise-shaping circuit performs residuesampling using back-to-back capacitors, and integrates residues bycharge sharing for signal-residue summation at the input side of thefine comparator.

In an exemplary embodiment, the first coarse comparator sets the firstset of successive-approximation registers in a first phase, and the finecomparator sets the first set of successive-approximation registers in asecond phase. The first phase is prior to the second phase.

In an exemplary embodiment, the second coarse comparator sets the secondset of successive-approximation registers in the second phase, and thefine comparator sets the second set of successive-approximationregisters in a third phase. The second phase is prior to the thirdphase.

In an exemplary embodiment, the first coarse comparator sets the firstset of successive-approximation registers in the third phase, and thefine comparator sets the first set of successive-approximation registersin a fourth phase. The third phase is prior to the fourth phase.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thesubsequent detailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 depicts a time-interleaved noise-shaping successive-approximationanalog-to-digital converter (TI NS-SAR ADC) 100 in accordance with anexemplary embodiment of the present invention;

FIG. 2 is a timing scheme for operating the TI NS-SAR ADC 100, and howthe noise-shaping circuit operates is shown; and

FIGS. 3A, 3B, 3C and 3D show the detailed connections of thenoise-shaping circuit in the four different phases Phase_1 to Phase_4.

DETAILED DESCRIPTION OF THE INVENTION

The following description shows exemplary embodiments carrying out theinvention. This description is made for the purpose of illustrating thegeneral principles of the invention and should not be taken in alimiting sense. The scope of the invention is best determined byreference to the appended claims.

To enlarge the bandwidth and increase SNR, a time-interleavednoise-shaping successive-approximation analog-to-digital converter (TINS-SAR ADC) is proposed. In an exemplary embodiment, a fully passivetime-interleaved noise-shaping technique is introduced to enable apower-efficient ADC for wideband and low-noise data conversion.

Note that if two channels are interleaved without additional processing,the residues are not available at the beginning in eachanalog-to-digital conversion phase and noise shaping fails. In theproposed architecture, after the first few bit cycles of SAR conversionof one channel, a residue from another channel is available. As aresult, each channel is able to complete the analog-to-digitalconversion with the correct residue.

FIG. 1 depicts a time-interleaved noise-shaping successive-approximationanalog-to-digital converter (TI NS-SAR ADC) 100 in accordance with anexemplary embodiment of the present invention. The TI NS-SAR ADC 100 hasa first successive-approximation channel CH1, a secondsuccessive-approximation channel CH2, a fine comparator Comp_F, anoise-shaping circuit (including the eight capacitors C1 to C8, a pairof integral capacitors C_(INTP), and C_(INTN), and the switchescontrolling the capacitors C1˜C8, C_(INTP), and C_(INTN)), and a decoderDEC. An input signal V_(I) (referring to the differential inputs V_(IP)and V_(IN)) of the TI NS-SAR 100 is sampled into the firstsuccessive-approximation channel CH1 and the secondsuccessive-approximation channel CH2 alternately, and the decoder DECoutputs digital representations DOUT of the input signal VI.

The first successive-approximation channel CH1 includes a firstcapacitive digital-to-analog converter (CDAC) CDAC1, a first coarsecomparator Comp_C1, and a first set of successive-approximationregisters (e.g., SAR logic) SAR_L1. The second successive-approximationchannel CH2 includes a second capacitive digital-to-analog converterCDAC2, a second coarse comparator Comp_C2, and a second set ofsuccessive-approximation registers (e.g., another SAR logic) SAR_L2.

The first capacitive digital-to-analog converter CDAC1 has a firstcapacitor network CN1 whose top plate INP1 is coupled to a positiveinput terminal of the first coarse comparator Comp_C1 and a secondcapacitor network CN2 whose top plate INN1 is coupled to a negativeinput terminal of the first coarse comparator Comp_C1. In the inputsampling phase of the first successive-approximation channel CH1, theinput signal V_(I) of the TI NS-SAR ADC 100 is sampled between the topplate INP1 of the first capacitor network CN1 and the top plate INN1 ofthe second capacitor network CN2. The first coarse comparator Comp_C1 isoperative to coarsely adjust the first set of successive-approximationregisters SAR_L1. The noise-shaping circuit and the fine comparatorComp_F are responsible to the fine adjustments of the first set ofsuccessive-approximation registers SAR_L1. The values of the first setof successive-approximation registers SAR_L1 are fed back to control thefirst capacitive digital-to-analog converter CDAC1. A circuit loop isformed for the successive-approximation in the firstsuccessive-approximation channel CH1.

The second capacitive digital-to-analog converter CDAC2 has a thirdcapacitor network CN3 whose top plate INP2 is coupled to a positiveinput terminal of the second coarse comparator Comp_C2 and a fourthcapacitor network CN4 whose top plate INN2 is coupled to a negativeinput terminal of the first coarse comparator Comp_C2. In an inputsampling phase of the second successive-approximation channel CH2, theinput signal V_(I) of the TI NS-SAR ADC 100 is sampled between the topplate INP2 of the third capacitor network CN3 and the top plate INN2 ofthe fourth capacitor network CN4. The second coarse comparator Comp_C2is operative to coarsely adjust the second set ofsuccessive-approximation registers SAR_L2. The noise-shaping circuit andthe fine comparator Comp_F are further responsible to the fineadjustments of the second set of successive-approximation registersSAR_L2. The values of the second set of successive-approximationregisters SAR_L2 are fed back to control the second capacitivedigital-to-analog converter CDAC2. A circuit loop is formed for thesuccessive-approximation in the second successive-approximation channelCH2.

The first successive-approximation channel CH1 and the secondsuccessive-approximation channel CH2 operate in an interleaved way.Specifically, the fine comparator Comp_F is shared by the firstsuccessive-approximation channel CH1 and the secondsuccessive-approximation channel CH2 to finely adjust the first set ofsuccessive-approximation registers SAR_L1 and the second set ofsuccessive-approximation registers SAR_L2 alternately. Sharing the finecomparator Comp_F not only saves hardware but also converts overallchannel offset into offset between the coarse and fine comparators(between Comp_C1 and Comp_F, or between Comp_C2 and Comp_F), preventingthe analog-to-digital conversion from overloading and mitigating errorsdue to channel mismatch.

Note that the fine comparator Comp_F and the noise-shaping circuitperfectly eliminate residues. The coarse-fine architecture furthersolves the non-causality of inter-channel residue exchange. Thenoise-shaping circuit samples residues (between INP1 and INN1) of thefirst successive-approximation channel CH1 and, accordingly, the finecomparator Comp_F finely adjusts the second set ofsuccessive-approximation registers SAR_L2. The noise-shaping circuitfurther samples residues (between INP2 and INN2) of the secondsuccessive-approximation channel CH2 and, accordingly, the finecomparator Comp_F finely adjusts the first set ofsuccessive-approximation registers SAR_L1. The residues are ready whenthe fine comparator Comp_F operates. The fine comparator Comp_F operatesbased on reliable residue information.

For each round of the setting of the successive-approximation registersSAR_L1/SAR_L2, the coarse comparator Comp_C1/Comp_C2 resolves theinitial bits at high speed, and then the low-noise fine comparatorComp_F resolves the lower bits and processes the signal-residuesummation. Since the coarse comparisons (Comp_C1 and Comp_C2) only workon the input signal without the residue (not ready), this arrangementallows another channel to have more time to finish the conversion andgenerate the residue. Once the residue is available and is charge sharedfor integration, the fine comparator Comp_f resolves the signal-residuesummation to achieve noise shaping.

The noise-shaping circuit may perform residue sampling by back-to-backcapacitors, and integrate residues by charge sharing, for signal-residuesummation at an input side (referring to VRP and VRN) of the finecomparator Comp_F. The sampled residue is 2× larger than that thatsampled by only one capacitor and no amplification is required. Theresidue is put in series with the capacitive digital-to-analog converterCDAC1/CDAC2 to realize summation.

The noise-shaping circuit may be a fully-passive design. In FIG. 1, thenoise-shaping circuit has eight capacitors C1 to C8, a pair of integralcapacitors C_(INTP), and C_(INTN), and the switches controlling thecapacitors C1˜C8, C_(INTP), and C_(INTN). As shown, the first integralcapacitor CINTP has a top plate coupled to a positive input terminal VRPof the fine comparator Comp_F, and the second integral capacitor CINTNhas a top plate coupled to a negative input terminal VRN of the finecomparator Comp_F. The first integral capacitor CINTP and the secondintegral capacitor CINTN are provided for integration of residuessampled from the first successive-approximation channel CH1 and thesecond successive-approximation channel CH2.

FIG. 2 is a timing scheme for operating the TI NS-SAR ADC 100, and howthe noise-shaping circuit operates is shown.

The waveforms shown in FIG. 2 are defined in this paragraph. CLKS1 isthe sampling clock of the first successive-approximation channel CH1.CLKC1 is the coarse comparison clock controlling the first coarsecomparator Comp_C1. Φ_(CH1, 1) controls the first and second capacitorsC1 and C2 to work as a pair of back-to-back capacitors for residuesampling of the first successive-approximation channel CH1. Φ_(CH1, 2)controls the fifth and sixth capacitors C5 and C6 to work as a pair ofback-to-back capacitors for residue sampling of the firstsuccessive-approximation channel CH1, interleaved with Φ_(CH1, 1). CLKS2is the sampling clock of the second successive-approximation channelCH2. CLKC2 is the coarse comparison clock signal controlling the secondcoarse comparator Comp_C2. Φ_(CH2, 1) controls the seventh and eighthcapacitors C7 and C8 to work as a pair of back-to-back capacitors forresidue sampling of the second successive-approximation channel CH2.Φ_(CH2, 1) controls the third and fourth capacitors C3 and C4 to work asa pair of back-to-back capacitors for residue sampling of the secondsuccessive-approximation channel CH2, interleaved with Φ_(CH2, 1). CLKFis the fine comparison clock controlling the fine comparator Comp_F.Φ_(Fine, 1) is operative to connect the first capacitivedigital-to-analog converter CDAC1 to the first and second integralcapacitors C_(INTP) and C_(INTN) to form a SAR loop for the firstsuccessive-approximation channel CH1. Φ_(Fine, 2) is operative toconnect the second capacitive digital-to-analog converter CDAC2 to thefirst and second integral capacitors CINTP and CINTN to form a SAR loopfor the second successive-approximation channel CH2. Φ_(RES CH1, 2)controls the charge sharing between the first integral capacitor CINTPand the fifth capacitor C5, and controls the charge sharing between thesecond integral capacitor C_(INTN) and the sixth capacitor C6.Φ_(RES CH2, 1) controls the charge sharing between the first integralcapacitor C_(INTP) and the seventh capacitor C7, and controls the chargesharing between the second integral capacitor C_(INTN) and the eighthcapacitor C8. Φ_(RES CH1, 1) controls the charge sharing between thefirst integral capacitor CINTP and the first capacitor C1, and controlsthe charge sharing between the second integral capacitor CINTN and thesecond capacitor C2. Φ_(RES CH2, 2) controls the charge sharing betweenthe first integral capacitor CINTP and the third capacitor C3, andcontrols the charge sharing between the second integral capacitor CINTNand the fourth capacitor C4. Φ_(RES CH1, 2), Φ_(RES CH2, 1),Φ_(RES CH1, 1), and Φ_(RES CH2, 2) are arranged to provide reliableresidues to the signal-residue summation.

The TI NS-SAR ADC 100 operates in four phases Phase_1, Phase_2, Phase_3and Phase_4. The first phase Phase_1 is prior to the second phasePhase_2, the second phase Phase_2 is prior to the third phase Phase_3,and the third phase Phase_3 is prior to the fourth phase Phase_4. Thefirst coarse comparator Comp_C1 sets the first set ofsuccessive-approximation registers SAR_L1 in the first phase Phase_1(referring to CLKC1) for the coarse adjustment of SAR_L1, and the finecomparator Comp_F sets the first set of successive-approximationregisters SAR_L1 in the second phase Phase_2 (referring to CLKF andΦ_(Fine, 1)) for the fine adjustment of SAR_L1. The second coarsecomparator Comp_C2 sets the second set of successive-approximationregisters SAR_L2 in the second phase Phase_2 (referring to CLKC2) forthe coarse adjustment of SAR_L2, and the fine comparator Comp_F sets thesecond set of successive-approximation registers SAR_L2 in the thirdphase Phase_3 (referring to CLKF and Φ_(Fine, 2)) for the fineadjustment of SAR_L2. The first coarse comparator Comp_C1 further setsthe first set of successive-approximation registers SAR_L1 in the thirdphase Phase_3 (referring to CLKC1) for the coarse adjustment of SAR_L1,and the fine comparator Comp_F sets the first set ofsuccessive-approximation registers SAR_L1 in the fourth phase Phase_4(referring to CLKF and Φ_(Fine, 1)) for the fine adjustment of SAR_L1.

At the end of the second phase Phase_2, an estimation of residue of thefirst successive-approximation channel CH1 is completed (due to thecoarse adjustment for SAR_L1 in the first phase Phase_1 and the fineadjustment for SAR_L1 in the second phase Phase_2) and sampled by thefirst and second capacitors C1 and C2 (referring to Φ_(CH1, 1)). Thefollowing fine comparison for the second successive-approximationchannel CH2 (referring to Φ_(Fine, 2)) in the third phase Phase_3,therefore, is based on the reliable residue value sampled in the firstand second capacitors C1 and C2 (referring to Φ_(RES CH1, 1)). At theend of the third phase Phase_3, an estimation of residue of the secondsuccessive-approximation channel CH2 is completed (due to the coarseadjustment for SAR_L2 in the second phase Phase_2 and the fineadjustment for SAR_L2 in the third phase Phase_3) and sampled by thethird and fourth capacitors C3 and C4 (referring to Φ_(CH2, 2)). Thefollowing fine comparison for the first successive-approximation channelCH1 (referring to Φ_(Fine, 1)) in the fourth phase Phase_4, therefore,is based on the reliable residue value sampled in the third and fourthcapacitors C3 and C4 (referring to Φ_(RES CH2, 2)). Reliable residueelimination is achieved.

FIG. 2 further shows that the second coarse comparator Comp_C2 sets thesecond set of successive-approximation registers SAR_L2 in the fourthphase Phase_4 (referring to CLKC2), and the fine comparator Comp_F setsthe second set of successive-approximation registers SAR_L₂ in the firstphase Phase_1 (referring to CLK_F and Φ_(Fine, 2)). A time-interleavedscheme is completed by the four phases Phase_1˜Phase_4.

FIGS. 3A, 3B, 3C and 3D show the detailed connections of thenoise-shaping circuit in the four different phases Phase_1 to Phase_4.

FIG. 3A corresponds to the first phase Phase_1. The top plate INP1 ofthe first capacitor network CN1 is coupled to the top plate of the firstcapacitor C1 and the bottom plate of the second capacitor C2, and thetop plate INN1 of the second capacitor network CN2 is coupled to thebottom plate of the first capacitor C1 and the top plate of the secondcapacitor C2. The fifth capacitor C5 and the first integral capacitorC_(INTP) are coupled in parallel between the positive input terminal VRPof the fine comparator Comp_F and the top plate INP2 of the thirdcapacitor network CN3, and the sixth capacitor C6 and the secondintegral capacitor C_(INTN) are coupled in parallel between the negativeinput terminal VRN of the fine comparator Comp_F and the top plate INN2of the fourth capacitor network CN4. The top plate INP2 of the thirdcapacitor network CN3 is coupled to the top plate of the seventhcapacitor C7 and the bottom plate of the eighth capacitor C8, and thetop plate INN2 of the fourth capacitor network CN4 is coupled to thebottom plate of the seventh capacitor C7 and the top plate of the eighthcapacitor C8.

In the first phase Phase_1, the fine comparator Comp_F sets the secondset of successive-approximation registers SAR_L2 based on the reliableresidue sampled from the first successive-approximation channel CH1, andthe first coarse comparator Comp_C1 sets the first set ofsuccessive-approximation registers SAR_L1.

FIG. 3B corresponds to the second phase Phase_2. The top plate INP1 ofthe first capacitor network CN1 is coupled to the top plate of the firstcapacitor C1 and the bottom plate of the second capacitor C2, and thetop plate INN1 of the second capacitor network CN2 is coupled to thebottom plate of the first capacitor C1 and the top plate of the secondcapacitor C2. The seventh capacitor C7 and the first integral capacitorCINTP are coupled in parallel between the positive input terminal VRP ofthe fine comparator Comp_F and the top plate INP1 of the first capacitornetwork CN1, and the eighth capacitor C8 and the second integralcapacitor C_(INTN) are coupled in parallel between the negative inputterminal VRN of the fine comparator Comp_F and the top plate INN1 of thesecond capacitor network CN2. The top plate INP2 of the third capacitornetwork CN3 is coupled to the top plate of the third capacitor C3 andthe bottom plate of the fourth capacitor C4, and the top plate INN2 ofthe fourth capacitor network CN4 is coupled to the bottom plate of thethird capacitor C3 and the top plate of the fourth capacitor C4.

In the second phase Phase_2, the fine comparator Comp_F sets the firstset of successive-approximation registers SAR_L1 based on the reliableresidue sampled from the second successive-approximation channel CH2,and the second coarse comparator Comp_C2 sets the second set ofsuccessive-approximation registers SAR_L2.

FIG. 3C corresponds to the third phase Phase_3. The top plate INP1 ofthe first capacitor network CN1 is coupled to the top plate of the fifthcapacitor C5 and the bottom plate of the sixth capacitor C6, and the topplate INN1 of the second capacitor network CN2 is coupled to the bottomplate of the fifth capacitor C5 and the top plate of the sixth capacitorC6. The first capacitor C1 and the first integral capacitor C_(INTP) arecoupled in parallel between the positive input terminal VRP of the finecomparator Comp_F and the top plate INP2 of the third capacitor networkCN3, and the second capacitor C2 and the second integral capacitorC_(INTN) are coupled in parallel between the negative input terminal VRNof the fine comparator Comp_F and the top plate INN2 of the fourthcapacitor network CN4. The top plate INP2 of the third capacitor networkCN3 is coupled to the top plate of the third capacitor C3 and the bottomplate of the fourth capacitor C4, and the top plate INN2 of the fourthcapacitor network CN4 is coupled to the bottom plate of the thirdcapacitor C3 and the top plate of the fourth capacitor C4.

In the third phase Phase_3, the fine comparator Comp_F sets the secondset of successive-approximation registers SAR_L2 based on the reliableresidue sampled from the first successive-approximation channel CH1, andthe first coarse comparator Comp_C1 sets the first set ofsuccessive-approximation registers SAR_L1.

FIG. 3D corresponds to the fourth phase Phase_4. The top plate INP1 ofthe first capacitor network CN1 is coupled to the top plate of the fifthcapacitor C5 and the bottom plate of the sixth capacitor C6, and the topplate INN1 of the second capacitor network CN2 is coupled to the bottomplate of the fifth capacitor C5 and the top plate of the sixth capacitorC6. The third capacitor C3 and the first integral capacitor CINTP arecoupled in parallel between the positive input terminal VRP of the finecomparator Comp_F and the top plate INP1 of the first capacitor networkCN1, and the fourth capacitor C4 and the second integral capacitorC_(INTN) are coupled in parallel between the negative input terminal VRNof the fine comparator Comp_F and the top plate INN1 of the secondcapacitor network CN2. The top plate INP2 of the third capacitor networkCN3 is coupled to the top plate of the seventh capacitor C7 and thebottom plate of the eighth capacitor C8, and the top plate INN2 of thefourth capacitor network CN4 is coupled to the bottom plate of theseventh capacitor C7 and the top plate of the eighth capacitor C8.

In the fourth phase Phase_4, the fine comparator Comp_F sets the firstset of successive-approximation registers SAR_L1 based on the reliableresidue sampled from the second successive-approximation channel CH2,and the second coarse comparator Comp_C2 sets the second set ofsuccessive-approximation registers SAR_L2.

The aforementioned TI NS-SAR ADC 100 effectively improves the dynamicrange (DR) and doubles the bandwidth compared to a conventional singlechannel SAR ADC. The layout size is limited due to the shared finecomparator. Specifically, no multiple-input-pair comparators andamplifiers are required. Hence, the proposed architecture is able todeliver wide bandwidth with sufficient DR for Wifi 6 while deliveringexcellent power efficiency.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it should be understood that the invention isnot limited to the disclosed embodiments. On the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

What is claimed is:
 1. A time-interleaved noise-shapingsuccessive-approximation analog-to-digital converter, comprising: afirst successive-approximation channel, having a first set ofsuccessive-approximation registers and a first coarse comparator coupledto the first set of successive-approximation registers to coarselyadjust the first set of successive-approximation registers; a secondsuccessive-approximation channel, having a second set ofsuccessive-approximation registers and a second coarse comparatorcoupled to the second set of successive-approximation registers tocoarsely adjust the second set of successive-approximation registers; afine comparator, coupled to the first set of successive-approximationregisters and the second set of successive-approximation registers, tofinely adjust the first set of successive-approximation registers andthe second set of successive-approximation registers; and anoise-shaping circuit, sampling residues of the firstsuccessive-approximation channel for the fine comparator to finelyadjust the second set of successive-approximation registers, andsampling residues of the second successive-approximation channel for thefine comparator to finely adjust the first set ofsuccessive-approximation registers.
 2. The time-interleavednoise-shaping successive-approximation analog-to-digital converter asclaimed in claim 1, wherein: the noise-shaping circuit performs residuesampling using back-to-back capacitors; and the noise-shaping circuitintegrates residues by charge sharing, for signal-residue summation atan input side of the fine comparator.
 3. The time-interleavednoise-shaping successive-approximation analog-to-digital converter asclaimed in claim 1, wherein: the first coarse comparator sets the firstset of successive-approximation registers in a first phase; the finecomparator sets the first set of successive-approximation registers in asecond phase; and the first phase is prior to the second phase.
 4. Thetime-interleaved noise-shaping successive-approximationanalog-to-digital converter as claimed in claim 3, wherein: the secondcoarse comparator sets the second set of successive-approximationregisters in the second phase; the fine comparator sets the second setof successive-approximation registers in a third phase; and the secondphase is prior to the third phase.
 5. The time-interleaved noise-shapingsuccessive-approximation analog-to-digital converter as claimed in claim4, wherein: the first coarse comparator sets the first set ofsuccessive-approximation registers in the third phase; the finecomparator sets the first set of successive-approximation registers in afourth phase; and the third phase is prior to the fourth phase.
 6. Thetime-interleaved noise-shaping successive-approximationanalog-to-digital converter as claimed in claim 5, wherein: the secondcoarse comparator sets the second set of successive-approximationregisters in the fourth phase.
 7. The time-interleaved noise-shapingsuccessive-approximation analog-to-digital converter as claimed in claim6, wherein: the fine comparator sets the second set ofsuccessive-approximation registers in the first phase.
 8. Thetime-interleaved noise-shaping successive-approximationanalog-to-digital converter as claimed in claim 1, wherein thenoise-shaping circuit further comprises: a first integral capacitorwhose top plate is coupled to a positive input terminal of the finecomparator; and a second integral capacitor whose top plate is coupledto a negative input terminal of the fine comparator, wherein the firstintegral capacitor and the second integral capacitor are provided forintegration of residues sampled from the first successive-approximationchannel and the second successive-approximation channel.
 9. Thetime-interleaved noise-shaping successive-approximationanalog-to-digital converter as claimed in claim 8, wherein the firstsuccessive-approximation channel further has a first capacitivedigital-to-analog converter operated according to the first set ofsuccessive-approximation registers, wherein the first capacitivedigital-to-analog converter has a first capacitor network whose topplate is coupled to a positive input terminal of the first coarsecomparator and a second capacitor network whose top plate is coupled toa negative input terminal of the first coarse comparator; the secondsuccessive-approximation channel further has a second capacitivedigital-to-analog converter operated according to the second set ofsuccessive-approximation registers, wherein the second capacitivedigital-to-analog converter has a third capacitor network whose topplate is coupled to a positive input terminal of the second coarsecomparator and a fourth capacitor network whose top plate is coupled toa negative input terminal of the second coarse comparator; in an inputsampling phase of the first successive-approximation channel, an inputsignal of the time-interleaved noise-shaping successive-approximationanalog-to-digital converter is sampled between the top plate of thefirst capacitor network and the top plate of the second capacitornetwork; and in an input sampling phase of the secondsuccessive-approximation channel, the input signal of thetime-interleaved noise-shaping successive-approximationanalog-to-digital converter is sampled between the top plate of thethird capacitor network and the top plate of the fourth capacitornetwork.
 10. The time-interleaved noise-shaping successive-approximationanalog-to-digital converter as claimed in claim 9, wherein thenoise-shaping circuit further comprises a first capacitor and a secondcapacitor, wherein: in a first phase and a second phase, the top plateof the first capacitor network is coupled to a top plate of the firstcapacitor and a bottom plate of the second capacitor, and the top plateof the second capacitor network is coupled to a bottom plate of thefirst capacitor and a top plate of the second capacitor; in a thirdphase, the first capacitor and the first integral capacitor are coupledin parallel between the positive input terminal of the fine comparatorand the top plate of the third capacitor network, and the secondcapacitor and the second integral capacitor are coupled in parallelbetween the negative input terminal of the fine comparator and the topplate of the fourth capacitor network; and the first phase is prior tothe second phase, and the second phase is prior to the third phase. 11.The time-interleaved noise-shaping successive-approximationanalog-to-digital converter as claimed in claim 10, wherein thenoise-shaping circuit further comprises a third capacitor and a fourthcapacitor, wherein: in the second phase and the third phase, the topplate of the third capacitor network is coupled to a top plate of thethird capacitor and a bottom plate of the fourth capacitor, and the topplate of the fourth capacitor network is coupled to a bottom plate ofthe third capacitor and a top plate of the fourth capacitor; in a fourthphase, the third capacitor and the first integral capacitor are coupledin parallel between the positive input terminal of the fine comparatorand the top plate of the first capacitor network, and the fourthcapacitor and the second integral capacitor are coupled in parallelbetween the negative input terminal of the fine comparator and the topplate of the second capacitor network; and the third phase is prior tothe fourth phase.
 12. The time-interleaved noise-shapingsuccessive-approximation analog-to-digital converter as claimed in claim11, wherein the noise-shaping circuit further comprises a fifthcapacitor and a sixth capacitor, wherein: in the first phase, the fifthcapacitor and the first integral capacitor are coupled in parallelbetween the positive input terminal of the fine comparator and the topplate of the third capacitor network, and the sixth capacitor and thesecond integral capacitor are coupled in parallel between the negativeinput terminal of the fine comparator and the top plate of the fourthcapacitor network.
 13. The time-interleaved noise-shapingsuccessive-approximation analog-to-digital converter as claimed in claim12, wherein the noise-shaping circuit further comprises a seventhcapacitor and an eighth capacitor, wherein: in the second phase, theseventh capacitor and the first integral capacitor are coupled inparallel between the positive input terminal of the fine comparator andthe top plate of the first capacitor network, and the eighth capacitorand the second integral capacitor are coupled in parallel between thenegative input terminal of the fine comparator and the top plate of thesecond capacitor network.
 14. The time-interleaved noise-shapingsuccessive-approximation analog-to-digital converter as claimed in claim13, wherein: in the third phase and the fourth phase, the top plate ofthe first capacitor network is coupled to a top plate of the fifthcapacitor and a bottom plate of the sixth capacitor, and the top plateof the second capacitor network is coupled to a bottom plate of thefifth capacitor and a top plate of the sixth capacitor.
 15. Thetime-interleaved noise-shaping successive-approximationanalog-to-digital converter as claimed in claim 14, wherein: in thefirst phase and the fourth phase, the top plate of the third capacitornetwork is coupled to a top plate of the seventh capacitor and a bottomplate of the eighth capacitor, and the top plate of the fourth capacitornetwork is coupled to a bottom plate of the seventh capacitor and a topplate of the eighth capacitor.
 16. The time-interleaved noise-shapingsuccessive-approximation analog-to-digital converter as claimed in claim15, wherein: the first coarse comparator sets the first set ofsuccessive-approximation registers in the first phase; and the finecomparator sets the first set of successive-approximation registers inthe second phase.
 17. The time-interleaved noise-shapingsuccessive-approximation analog-to-digital converter as claimed in claim16, wherein: the second coarse comparator sets the second set ofsuccessive-approximation registers in the second phase; and the finecomparator sets the second set of successive-approximation registers inthe third phase.
 18. The time-interleaved noise-shapingsuccessive-approximation analog-to-digital converter as claimed in claim17, wherein: the first coarse comparator sets the first set ofsuccessive-approximation registers in the third phase; and the finecomparator sets the first set of successive-approximation registers inthe fourth phase.
 19. The time-interleaved noise-shapingsuccessive-approximation analog-to-digital converter as claimed in claim18, wherein: the second coarse comparator sets the second set ofsuccessive-approximation registers in the fourth phase.
 20. Thetime-interleaved noise-shaping successive-approximationanalog-to-digital converter as claimed in claim 19, wherein: the finecomparator sets the second set of successive-approximation registers inthe first phase.